U.S. Pat. No. 3,036,570 issued to H. T. Milgrom and W. T. Hewboski discloses a vaginal contraceptive diaphragm (pessary) having an integral inwardly projecting lip to provide increased retention thereof. An embedded toroidally wound spring peripherally disposed within a flange surrounding a central dome-shaped portion provides the principal retentive force, the spring being integrally molded to the flange during the manufacturing process, using conventional pressure molding techniques. The dome-like portion with an integral flange is first manufactured in a separate step by pressure molding, whereupon the spring is laid over an annular portion of the flange, and the second inwardly extending lip portion is formed therearound in a second molding operation wherein the lip is formed integrally attached to the flange of the diaphragm body, with the spring trapped there between.
This manufacturing process frequently results in the spring being carried completely to the edge of the structure because of molding pressures, resulting in a spring substantially off center, and close to, if not actually penetrating, the outer wall of the flange. Since the spring portion is routinely flexed in insertion, a possibility exists that a thin flange wall in the vicinity of the spring can result in a protruding spring, resulting in irritation to the user. Such defects are frequently observed during the manufacturing process, resulting in a substantial number of manufacturing rejects. Additionally, as will subsequently be discussed, this integral formation method leads to a substantial problem in extracting the finished diaphragm assembly from the injection mold, because of topological problems presented by the inwardly extending lip and spring rigidity.
Another difficulty arises from the fact that the spring has a specific heat substantially different from the elastomer from which the lip and flange are formed, with the result that it is difficult to get an adequate and uniform heating of the elastomer around the spring to provide adequate and uniform curing without causing local overcuring and concomitant embrittlement. Moreover, since the spring is embedded in the elastomer and has its windings interpenetrated by the elastomer during the molding process, the result is that the resulting structures so produced have quite variable spring tension properties, owing to the above mentioned curing problems, as well as the fact that the interpenetration by the elastomer is not subject to close control. A further feature of such a structure, wherein the spring is captively embedded in the flange, lies in its rigidity during insertion by the user, since the elastomer is not free to rotate at all about the toroidal spring. This is can be a source of discomfort.
Thus, it has been considered desirable that an improved manufacturing process be developed that would provide a more controllably curable assembly wherein no substantial lateral displacement of the spring occurs, with the associated danger of producing an unacceptably thin outer wall. A process that would yield a less rigid structure would also be desirable.